Electric engine cooling fan modules have become standard in most automobiles with front wheel drive. Depending on the application, single and dual fan engine cooling modules are used to provide engine cooling. In the past, single and dual speed fan modules have dominated the market. However, recently, variable speed motor drives have been implemented for single and dual cooling fan modules employing brush type motors to improve system efficiency.
Dual engine cooling fan modules have been in automobiles since the advent of electrodrive cooling fan modules in the previous decades. Single speed and dual speed variations of these modules exist which are capable of varying the amount of airflow delivered to engine through the switching arrangement of the motors. With reference to FIG. 1, one such arrangement 10 is the so called “series parallel connection” which uses relays 12 to switch motors M from a parallel connection to a series connection in order to achieve full speed and reduced speed operation.
Variable speed drives for dual fan arrangements have been in production since 1996. With reference to FIG. 2, these variable speed drive systems typically use pulse width modulation (PWM) to control the speed of the motors M, either independently, or together. A block diagram of a dual fan module 20 using simultaneous PWM control 14 for both motors M is shown in FIG. 2. Simultaneous control of both motors M is a cost-effective solution, in that the complexity of the control logic is reduced. In such a system, care should be taken to separate the maximum speed of both motors to prevent acoustic “beating”, or heterodyning.
A block diagram of a dual fan module 30 using independent PWM control 14′ for both motors M is shown in FIG. 3. For clarity, components such as DC link capacitors and radio frequency interference (RFI) suppression chokes have been excluded in FIGS. 2 and 3. Independent motor control has numerous benefits, including, better temperature control and increased fault tolerance due to the separation of the two motor power stages. Separate motor control can be more expensive than simultaneous motor control due to the cost of the control electronics.
Depending on the PWM switching strategy employed, there is a need to provide separate motor switching schemes that will result in lower stress on power stage components and lower conducted and radiated radio frequency emissions. Also, there is a need to lower conducted RFI emissions today's automobile since the electronic content in automobiles is increasing.